The present invention relates generally to laser devices and more particularly to an improved solid state laser for producing pulsed laser signals of good fidelity and controlled duration and power.
Previously, laser oscillators employing optical pumping have been operated in one of two modes: continuous (cw) or pulse. Inherently, optically pumped cw laser oscillators produce low output power. Therefore, the use of a shutter or other means to extract a laser pulse from a cw laser produces only a low power pulse. Pulsed optically pumped laser oscillators have previously taken two basic forms: the so-called normal-mode laser, in which oscillation grows spontaneously during optical pumping and then terminates before the pumping pulse is completed; and the so-called Q-switched mode, in which oscillation, having been suppressed during a large part of the pumping pulse, grows very rapidly, after switching, to a high power for a small fraction of the total pumping time and then rapidly decays. Although adjustment of pump power can influence emitted power and pulse duration in a somewhat predicted way, neither power distribution during the emission time nor the pulse duration can be accurately controlled in either mode.
Optically pumped laser amplifiers have generally functioned primarily as energy amplifiers and, as such, have previously been operated in such a way as to saturate the gain. That is to say, amplification of the early part of a pulse depletes the energy stored by optical pumping so that later parts of the pulse are amplified less; the trailing edge of the pulse, in general, is not amplified at all. Saturation of the gain makes preservation of the pulse shape difficult, if not impossible. At the same time, to achieve high pulse-energy efficiency, the small signal gain must be made large. This means that spontaneous photons may be amplified, causing still further distortion. In some situations, spurious oscillations will occur, severely depleting the population inversion.
There has long existed the need for a laser in which both the duration of the emitted pulse and its power level can be accurately controlled. This need exists, for example, in certain illumination devices, in applications requiring fixed rates of energy transfer (e.g., medical applications) and in communications systems, to name a few. The satisfaction of this need would require laser oscillators that produce well shaped, generally rectangular pulses of controlled power, and amplifiers that provide both gain and fidelity.